diff --git a/php-transformer/CHANGELOG.md b/php-transformer/CHANGELOG.md
index b37ce6c4..a8196fdc 100644
--- a/php-transformer/CHANGELOG.md
+++ b/php-transformer/CHANGELOG.md
@@ -2,6 +2,15 @@
 
 All notable changes to this project will be documented in this file. Entries are generated by homeboy from git commits.
 
+## [0.4.17] - 2026-08-14
+
+### Added
+- Expose separate `source: engine-support` CSS assets with `stylesheet_placement` values `before-author` and `after-author`; mark `source: author-css` assets with `author`
+
+### Fixed
+- Neutralize constrained-layout geometry on direct children of `blocks-engine-css-owned-layout`
+- Make rich-text marker inline color and background resets self-sufficient
+
 ## [0.4.16] - 2026-08-12
 
 ### Added
diff --git a/php-transformer/VERSION b/php-transformer/VERSION
index 5745cc7b..7040b811 100644
--- a/php-transformer/VERSION
+++ b/php-transformer/VERSION
@@ -1 +1 @@
-0.4.16
+0.4.17
diff --git a/php-transformer/composer.json b/php-transformer/composer.json
index c90b7c89..d1388197 100644
--- a/php-transformer/composer.json
+++ b/php-transformer/composer.json
@@ -77,6 +77,7 @@
       "php tests/unit/css-stylesheet-transformer.php",
       "php tests/unit/css-selector-matcher.php",
       "php tests/unit/author-selector-semantics.php",
+      "php tests/unit/engine-support-css-asset.php",
       "php tests/unit/artifact-author-stylesheet-projection.php",
       "php tests/unit/fallback-finding-normalizer.php",
       "php tests/unit/navigation-underline-color-resolver.php",
diff --git a/php-transformer/php-transformer.php b/php-transformer/php-transformer.php
index 56b293c3..d8fce56f 100644
--- a/php-transformer/php-transformer.php
+++ b/php-transformer/php-transformer.php
@@ -3,7 +3,7 @@
  * Plugin Name: Blocks Engine PHP Transformer
  * Plugin URI: https://github.com/Automattic/blocks-engine/tree/trunk/php-transformer
  * Description: Canonical PHP primitives for transforming HTML, Markdown, and website artifacts into WordPress block outputs.
- * Version: 0.4.16
+ * Version: 0.4.17
  * Requires PHP: 8.1
  * Author: Automattic
  * License: GPL-3.0-or-later
@@ -15,7 +15,7 @@
 declare(strict_types=1);
 
 if ( ! defined('BLOCKS_ENGINE_PHP_TRANSFORMER_VERSION') ) {
-    define('BLOCKS_ENGINE_PHP_TRANSFORMER_VERSION', '0.4.16');
+    define('BLOCKS_ENGINE_PHP_TRANSFORMER_VERSION', '0.4.17');
 }
 
 if ( ! defined('BLOCKS_ENGINE_PHP_TRANSFORMER_FILE') ) {
diff --git a/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php b/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php
index 88f6c520..38c77dbd 100644
--- a/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php
+++ b/php-transformer/src/ArtifactCompiler/ArtifactCompiler.php
@@ -219,18 +219,14 @@ public function compile(array $artifact): TransformerResult
         $wordpressCompatAsset = $this->wordpressCompatAsset($normalized['files']);
         $referenceReports = $this->referenceReports($normalized['files']);
         $manifestAssets = $this->assetManifest($normalized['files'], $entryPath, $referenceReports['asset_references'], $html);
-        $geometryAssets = array_values(array_filter($entryBlocks['assets'], static fn (array $asset): bool => 'css' === ($asset['kind'] ?? '') && str_contains((string) ($asset['content'] ?? ''), '.be-inline-geometry-')));
-        $otherGeneratedAssets = array_values(array_filter($entryBlocks['assets'], static fn (array $asset): bool => ! in_array($asset, $geometryAssets, true)));
-        if ( is_array($entry) ) {
-            $entryOwnership = $this->fileOwnership($entry);
-            foreach ( $geometryAssets as &$generatedAsset ) $generatedAsset['compilation'] ??= $entryOwnership;
-            unset($generatedAsset);
-            foreach ( $otherGeneratedAssets as &$generatedAsset ) if ('css' === ($generatedAsset['kind'] ?? null)) $generatedAsset['compilation'] ??= $entryOwnership;
-            unset($generatedAsset);
-        }
-        // Runtime loads the manifest in array order. Put carrier CSS before
-        // authored assets so authored !important declarations preserve cascade.
-        $assets = array_merge($geometryAssets, $manifestAssets, $otherGeneratedAssets);
+        $entryOwnership = is_array($entry) ? $this->fileOwnership($entry) : array('scope' => 'page', 'id' => $entryPath);
+        $generatedAssets = $this->generatedAssetsForDocuments($entryBlocks['assets'], $entryOwnership, $compiledHtmlDocuments, $normalized['files']);
+        $beforeAuthorAssets = array_values(array_filter($generatedAssets, static fn (array $asset): bool => 'before-author' === ($asset['stylesheet_placement'] ?? '')));
+        $afterAuthorAssets = array_values(array_filter($generatedAssets, static fn (array $asset): bool => 'after-author' === ($asset['stylesheet_placement'] ?? '')));
+        $otherGeneratedAssets = array_values(array_filter($generatedAssets, static fn (array $asset): bool => ! in_array($asset, $beforeAuthorAssets, true) && ! in_array($asset, $afterAuthorAssets, true)));
+        // Runtime loads the manifest in array order. Placement metadata keeps
+        // engine support on its intended side of the authored stylesheets.
+        $assets = array_merge($beforeAuthorAssets, $manifestAssets, $otherGeneratedAssets, $afterAuthorAssets);
         if ( null !== $wordpressCompatAsset ) {
             $assets[] = $wordpressCompatAsset;
         }
@@ -434,6 +430,60 @@ private function fileOwnership(array $file): array
         return array('scope' => 'page', 'id' => $ownership['id']);
     }
 
+    /**
+     * @param array<int,array<string,mixed>> $entryAssets
+     * @param array{scope:string,id:string} $entryOwnership
+     * @param array<string,array<string,mixed>> $compiledHtmlDocuments
+     * @param array<int,array<string,mixed>> $files
+     * @return array<int,array<string,mixed>>
+     */
+    private function generatedAssetsForDocuments(array $entryAssets, array $entryOwnership, array $compiledHtmlDocuments, array $files): array
+    {
+        $assets = array();
+        $assetIndexes = array();
+        $append = static function (array $documentAssets, array $ownership) use (&$assets, &$assetIndexes): void {
+            foreach ( $documentAssets as $asset ) {
+                if ( ! is_array($asset) ) {
+                    continue;
+                }
+                if ( 'css' === ($asset['kind'] ?? null) ) {
+                    $asset['compilation'] ??= $ownership;
+                }
+                $payload = is_string($asset['content_base64'] ?? null) ? $asset['content_base64'] : (string) ($asset['content'] ?? '');
+                $identity = hash('sha256', (string) ($asset['path'] ?? '') . "\0" . $payload);
+                if ( ! isset($assetIndexes[$identity]) ) {
+                    $assetIndexes[$identity] = count($assets);
+                    $assets[] = $asset;
+                    continue;
+                }
+                $index = $assetIndexes[$identity];
+                if ( 'css' !== ($asset['kind'] ?? null) ) {
+                    continue;
+                }
+                $existingOwnership = $assets[$index]['compilation'] ?? null;
+                $assetOwnership = $asset['compilation'] ?? null;
+                if ( $existingOwnership !== $assetOwnership ) {
+                    $assets[$index]['compilation'] = array('scope' => 'shared');
+                }
+            }
+        };
+
+        $append($entryAssets, $entryOwnership);
+        $filesByPath = array_column($files, null, 'path');
+        foreach ( $compiledHtmlDocuments as $sourcePath => $compiledHtmlDocument ) {
+            $file = $filesByPath[$sourcePath] ?? array('path' => $sourcePath, 'kind' => 'html');
+            $append(
+                array_values(array_filter(
+                    is_array($compiledHtmlDocument['assets'] ?? null) ? $compiledHtmlDocument['assets'] : array(),
+                    static fn (array $asset): bool => 'css' === ($asset['kind'] ?? null)
+                )),
+                $this->fileOwnership($file)
+            );
+        }
+
+        return $assets;
+    }
+
     /**
      * @param array{entrypoints:array<int,string>,limits:array<string,int>,runtime_declarations:array<int,array<string,mixed>>,schema:string,input_keys:array<int,string>} $partition
      * @param array<int,array<string,mixed>> $files
@@ -3404,6 +3454,7 @@ private function compiledSiteAssets(array $assets): array
                     'target_path'      => $asset['target_path'] ?? $asset['path'] ?? '',
                     'kind'             => $asset['kind'] ?? '',
                     'role'             => $asset['role'] ?? '',
+                    'stylesheet_placement' => $asset['stylesheet_placement'] ?? '',
                     'intent'           => $asset['intent'] ?? '',
                     'media_type'       => $asset['media_type'] ?? $asset['mime_type'] ?? '',
                     'media'            => $asset['media'] ?? '',
diff --git a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
index f28cc488..18c3a8c6 100644
--- a/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
+++ b/php-transformer/src/HtmlToBlocks/HtmlTransformer.php
@@ -1033,13 +1033,15 @@ private function headMetadataReport(string $html): array
 
     private function materializeAuthorStylesheet(string $html, string $staticCss, bool $includeAuthorStyles = true, string $serializedBlocks = ''): void
     {
-        $cssParts = array();
+        $beforeAuthorCssParts = array();
+        $authorCssParts = array();
+        $afterAuthorCssParts = array();
         $authorCss = '';
         if ( $includeAuthorStyles && '' !== $this->combinedAuthorCss ) {
             $authorCss = $this->rewriteAuthorStylesheet($this->combinedAuthorCss);
             $split = ( new CssStylesheetTransformer() )->splitLeadingAtRulePreamble($authorCss);
             if ( '' !== trim($split['preamble']) ) {
-                $cssParts[] = $split['preamble'];
+                $authorCssParts[] = $split['preamble'];
             }
             $authorCss = $split['stylesheet'];
         }
@@ -1048,79 +1050,87 @@ private function materializeAuthorStylesheet(string $html, string $staticCss, bo
             // Important carrier rules precede author CSS: they retain inline
             // precedence over normal selectors while authored !important rules
             // remain able to override them.
-            $cssParts[] = $geometryCss;
+            $beforeAuthorCssParts[] = $geometryCss;
         }
         $markerReset = $this->richTextMarkerResetCss();
         if ( '' !== $markerReset ) {
-            $cssParts[] = $markerReset;
+            $beforeAuthorCssParts[] = $markerReset;
         }
         if ( str_contains($serializedBlocks, self::SYNTHETIC_PARAGRAPH_CLASS) ) {
             // A paragraph is required for valid block markup, but phrasing content
             // did not have paragraph margins in the source document.
-            $cssParts[] = ':where(.' . self::SYNTHETIC_PARAGRAPH_CLASS . '){margin-top:0;margin-bottom:0}'
+            $beforeAuthorCssParts[] = ':where(.' . self::SYNTHETIC_PARAGRAPH_CLASS . '){margin-top:0;margin-bottom:0}'
                 . "\n" . ':where(p.' . self::SYNTHETIC_PARAGRAPH_CLASS . ')>a{text-decoration:underline}'
                 . "\n" . ':where(p.' . self::SYNTHETIC_PARAGRAPH_CLASS . '.' . self::SYNTHETIC_ANCHOR_UNDECORATED_CLASS . ')>a{text-decoration:none}';
         }
         if ( str_contains($serializedBlocks, self::INLINE_LAYOUT_CARRIER_CLASS) ) {
-            $cssParts[] = ':where(p.' . self::INLINE_LAYOUT_CARRIER_CLASS . '){display:contents;margin:0!important;padding:0!important;border:0!important}';
+            $beforeAuthorCssParts[] = ':where(p.' . self::INLINE_LAYOUT_CARRIER_CLASS . '){display:contents;margin:0!important;padding:0!important;border:0!important}';
         }
         if ( str_contains($serializedBlocks, self::CSS_OWNED_FLOW_CLASS) ) {
-            $cssParts[] = ':where(.' . self::CSS_OWNED_FLOW_CLASS . ')>p{margin-top:0;margin-bottom:0}';
+            $beforeAuthorCssParts[] = ':where(.' . self::CSS_OWNED_FLOW_CLASS . ')>p{margin-top:0;margin-bottom:0}';
         }
         if ( str_contains($serializedBlocks, self::POSITIONED_FRAGMENT_LINK_CARRIER_CLASS) ) {
             // Positioned fragment links retain their source anchor and selectors;
             // their valid paragraph host must not create a line box in document flow.
-            $cssParts[] = ':where(.' . self::POSITIONED_FRAGMENT_LINK_CARRIER_CLASS . '){display:contents!important}';
+            $beforeAuthorCssParts[] = ':where(.' . self::POSITIONED_FRAGMENT_LINK_CARRIER_CLASS . '){display:contents!important}';
         }
         if ( str_contains($serializedBlocks, self::EMPTY_FLEX_ITEM_CLASS) ) {
-            $cssParts[] = ':where(.' . self::EMPTY_FLEX_ITEM_CLASS . '){flex:0 0 0!important;width:0!important;min-width:0!important;margin-left:0!important;margin-right:0!important}';
+            $beforeAuthorCssParts[] = ':where(.' . self::EMPTY_FLEX_ITEM_CLASS . '){flex:0 0 0!important;width:0!important;min-width:0!important;margin-left:0!important;margin-right:0!important}';
         }
         if ( str_contains($serializedBlocks, self::CSS_OWNED_FLOW_CLASS) ) {
             // Core flow spacing is not part of a source grid or flex contract.
             // This precedes author CSS so source child margins remain authoritative.
-            $cssParts[] = ':where(.wp-block-group.' . self::CSS_OWNED_FLOW_CLASS . ')>*{margin-block-start:0;margin-block-end:0}';
+            $beforeAuthorCssParts[] = ':where(.wp-block-group.' . self::CSS_OWNED_FLOW_CLASS . ')>*{margin-block-start:0;margin-block-end:0}';
         }
         if ( str_contains($serializedBlocks, self::CSS_OWNED_GRID_CLASS) ) {
             // Core flow margins are not part of a source grid contract; the
             // carried grid geometry (gap) owns the spacing between items. The
             // carrier rides groups and lists, so the reset is class-scoped.
-            $cssParts[] = ':where(.' . self::CSS_OWNED_GRID_CLASS . ')>*{margin-block-start:0;margin-block-end:0}';
+            $beforeAuthorCssParts[] = ':where(.' . self::CSS_OWNED_GRID_CLASS . ')>*{margin-block-start:0;margin-block-end:0}';
         }
         if ( str_contains($serializedBlocks, self::CSS_OWNED_LAYOUT_ITEM_CLASS) ) {
             // A semantic Group used as a direct grid/flex item contains native
             // paragraph blocks. Neutralize only those generated inner defaults.
-            $cssParts[] = ':where(.wp-block-group.' . self::CSS_OWNED_LAYOUT_ITEM_CLASS . ')>*{margin-block-start:0;margin-block-end:0}';
+            $beforeAuthorCssParts[] = ':where(.wp-block-group.' . self::CSS_OWNED_LAYOUT_ITEM_CLASS . ')>*{margin-block-start:0;margin-block-end:0}';
         }
         if ( str_contains($serializedBlocks, 'blocks-engine-list-navigation') ) {
-            $cssParts[] = '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation-item.wp-block-navigation-link{display:list-item;font:inherit}'
+            $beforeAuthorCssParts[] = '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation-item.wp-block-navigation-link{display:list-item;font:inherit}'
                 . "\n" . '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation-item__content{display:inline}';
         }
         if ( array() !== $this->nativeSearchTriggerCssRules ) {
-            $cssParts[] = implode("\n", $this->nativeSearchTriggerCssRules);
+            $beforeAuthorCssParts[] = implode("\n", $this->nativeSearchTriggerCssRules);
         }
         if ( '' !== trim($authorCss) ) {
-            $cssParts[] = $authorCss;
+            $authorCssParts[] = $authorCss;
         }
         if ( str_contains($serializedBlocks, 'blocks-engine-list-navigation') ) {
             // The source mobile menu hides its desktop list container. Core
             // navigation owns that responsive swap now, so keep the block host
             // visible and let core hide only its responsive inner container.
-            $cssParts[] = '.wp-block-navigation.blocks-engine-list-navigation{display:flex!important}';
+            $afterAuthorCssParts[] = '.wp-block-navigation.blocks-engine-list-navigation{display:flex!important}';
             $mobileOverlayBackground = $this->sourceMobileNavigationOverlayBackground();
             if ( '' !== $mobileOverlayBackground ) {
-                $cssParts[] = '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation__responsive-container.is-menu-open{background:' . $mobileOverlayBackground . '!important}';
+                $afterAuthorCssParts[] = '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation__responsive-container.is-menu-open{background:' . $mobileOverlayBackground . '!important}';
             }
         }
         if ( array() !== $this->nativeButtonStyleRules ) {
-            $cssParts[] = implode("\n", $this->nativeButtonStyleRules);
+            $afterAuthorCssParts[] = implode("\n", $this->nativeButtonStyleRules);
         }
         if ( array() !== $this->directFlexButtonStyleRules ) {
-            $cssParts[] = implode("\n", $this->directFlexButtonStyleRules);
+            $afterAuthorCssParts[] = implode("\n", $this->directFlexButtonStyleRules);
         }
         if ( array() !== $this->fullWidthButtonStyleRules ) {
-            $cssParts[] = implode("\n", $this->fullWidthButtonStyleRules);
+            $afterAuthorCssParts[] = implode("\n", $this->fullWidthButtonStyleRules);
         }
 
+        $this->materializeStylesheetAsset($beforeAuthorCssParts, 'engine-support', 'before-author', 'engine-support-before-author');
+        $this->materializeStylesheetAsset($authorCssParts, 'author-css', 'author', 'source-author');
+        $this->materializeStylesheetAsset($afterAuthorCssParts, 'engine-support', 'after-author', 'engine-support-after-author');
+    }
+
+    /** @param array<int, string> $cssParts */
+    private function materializeStylesheetAsset(array $cssParts, string $source, string $placement, string $pathPrefix): void
+    {
         $css = trim(implode("\n\n", $cssParts));
         if ( '' === $css ) {
             return;
@@ -1128,15 +1138,16 @@ private function materializeAuthorStylesheet(string $html, string $staticCss, bo
 
         $content = $css . "\n";
         $hash = hash('sha256', $content);
-        $path = 'assets/css/source-author-' . substr($hash, 0, 16) . '.css';
+        $path = 'assets/css/' . $pathPrefix . '-' . substr($hash, 0, 16) . '.css';
 
         $this->generatedAssets[$path] = array(
-            'source'      => 'author-css',
+            'source'      => $source,
             'source_path' => '',
             'path'        => $path,
             'target_path' => $path,
             'kind'        => 'css',
             'role'        => 'stylesheet',
+            'stylesheet_placement' => $placement,
             'mime_type'   => 'text/css',
             'media_type'  => 'text/css',
             'content'     => $content,
@@ -1435,14 +1446,8 @@ private function authorStylesheetAssetsFromOptions(array $options): array
     private function authorStylesheetProjections(): array
     {
         $projections = array();
-        $markerReset = $this->richTextMarkerResetCss();
         foreach ( $this->authorStylesheetAssets as $asset ) {
             $content = $this->rewriteAuthorStylesheet($asset['content']);
-            if ( '' !== $markerReset ) {
-                $split = ( new CssStylesheetTransformer() )->splitLeadingAtRulePreamble($content);
-                $content = $split['preamble'] . $markerReset . "\n" . $split['stylesheet'];
-                $markerReset = '';
-            }
             $hash = hash('sha256', $content);
             $projections[] = array(
                 'path'        => $asset['path'],
diff --git a/php-transformer/src/StaticSite/MaterializationPlanBuilder.php b/php-transformer/src/StaticSite/MaterializationPlanBuilder.php
index e8bdc161..effd2e13 100644
--- a/php-transformer/src/StaticSite/MaterializationPlanBuilder.php
+++ b/php-transformer/src/StaticSite/MaterializationPlanBuilder.php
@@ -282,6 +282,7 @@ private function assets(array $assets): array
                 'target_path'      => (string) ($asset['target_path'] ?? $asset['path'] ?? ''),
                 'kind'             => (string) ($asset['kind'] ?? ''),
                 'role'             => (string) ($asset['role'] ?? ''),
+                'stylesheet_placement' => (string) ($asset['stylesheet_placement'] ?? ''),
                 'intent'           => (string) ($asset['intent'] ?? ''),
                 'media_type'       => (string) ($asset['media_type'] ?? $asset['mime_type'] ?? ''),
                 'media'            => (string) ($asset['media'] ?? ''),
diff --git a/php-transformer/src/WordPressSitePlan/WordPressSitePlan.php b/php-transformer/src/WordPressSitePlan/WordPressSitePlan.php
index 994ece20..a1da06a3 100644
--- a/php-transformer/src/WordPressSitePlan/WordPressSitePlan.php
+++ b/php-transformer/src/WordPressSitePlan/WordPressSitePlan.php
@@ -497,7 +497,7 @@ private function assets(mixed $assets): array
             $reference = self::payloadReference($asset['payload_reference'] ?? null);
             if (null !== $reference && !self::referenceBackedBinaryAsset($asset)) throw new InvalidArgumentException('WordPress site plan payload references are limited to non-SVG binary assets.');
             $transportHash = is_string($asset['content_base64'] ?? null) ? self::contentHash($asset['content_base64']) : null;
-            $rows[] = array_filter(array('source_path' => $asset['path'], 'target_path' => $target, 'token' => 'asset-' . substr(hash('sha256', $target), 0, 16), 'source' => self::value($asset, 'source'), 'kind' => self::value($asset, 'kind'), 'role' => self::value($asset, 'role'), 'intent' => self::value($asset, 'intent'), 'mime_type' => self::value($asset, 'mime_type'), 'media' => self::value($asset, 'media'), 'bytes' => (int) ($asset['bytes'] ?? 0), 'hash' => self::value($asset, 'hash'), 'content' => $asset['content'] ?? null, 'content_base64' => $asset['content_base64'] ?? null, 'payload_reference' => $reference, 'raw_sha256' => $reference['sha256'] ?? ($asset['raw_sha256'] ?? null), 'transport_sha256' => $transportHash, 'binary' => ! empty($asset['binary']), 'compilation' => is_array($asset['compilation'] ?? null) ? $asset['compilation'] : null, 'reconciliation_identity' => self::identity('asset', $asset['path'], $target), 'content_hash' => $reference['sha256'] ?? self::contentHash($payload)), static fn(mixed $value): bool => null !== $value);
+            $rows[] = array_filter(array('source_path' => $asset['path'], 'target_path' => $target, 'token' => 'asset-' . substr(hash('sha256', $target), 0, 16), 'source' => self::value($asset, 'source'), 'kind' => self::value($asset, 'kind'), 'role' => self::value($asset, 'role'), 'stylesheet_placement' => self::value($asset, 'stylesheet_placement'), 'intent' => self::value($asset, 'intent'), 'mime_type' => self::value($asset, 'mime_type'), 'media' => self::value($asset, 'media'), 'bytes' => (int) ($asset['bytes'] ?? 0), 'hash' => self::value($asset, 'hash'), 'content' => $asset['content'] ?? null, 'content_base64' => $asset['content_base64'] ?? null, 'payload_reference' => $reference, 'raw_sha256' => $reference['sha256'] ?? ($asset['raw_sha256'] ?? null), 'transport_sha256' => $transportHash, 'binary' => ! empty($asset['binary']), 'compilation' => is_array($asset['compilation'] ?? null) ? $asset['compilation'] : null, 'reconciliation_identity' => self::identity('asset', $asset['path'], $target), 'content_hash' => $reference['sha256'] ?? self::contentHash($payload)), static fn(mixed $value): bool => null !== $value);
         }
         return $rows;
     }
diff --git a/php-transformer/tests/contract/run.php b/php-transformer/tests/contract/run.php
index b76e6aed..6f6258ef 100644
--- a/php-transformer/tests/contract/run.php
+++ b/php-transformer/tests/contract/run.php
@@ -2743,8 +2743,9 @@ public function match(DOMElement $element, PatternContext $context): ?array
 )->toArray();
 $artifactNonEntryInlineSvgPage = $artifactNonEntryInlineSvg['source_reports']['materialization_plan']['pages'][1] ?? array();
 $artifactNonEntryInlineSvgAssets = $artifactNonEntryInlineSvg['source_reports']['materialization_plan']['assets'] ?? array();
+$artifactNonEntryInlineSvgImageAssets = array_values(array_filter($artifactNonEntryInlineSvgAssets, static fn (array $asset): bool => 'svg' === ($asset['kind'] ?? '')));
 $assert(str_contains((string) ($artifactNonEntryInlineSvgPage['block_markup'] ?? ''), '<!-- wp:image'), 'non-entry artifact simple icon SVG is represented as native core/image, not a dynamic core/icon');
-$assert(str_contains((string) ($artifactNonEntryInlineSvgAssets[0]['content'] ?? ''), 'aria-label="About icon"') && str_contains((string) ($artifactNonEntryInlineSvgAssets[0]['content'] ?? ''), 'viewBox="0 0 8 8"'), 'non-entry artifact faithful SVG preserves its accessible label and correct-case viewBox in the generated asset');
+$assert(str_contains((string) ($artifactNonEntryInlineSvgImageAssets[0]['content'] ?? ''), 'aria-label="About icon"') && str_contains((string) ($artifactNonEntryInlineSvgImageAssets[0]['content'] ?? ''), 'viewBox="0 0 8 8"'), 'non-entry artifact faithful SVG preserves its accessible label and correct-case viewBox in the generated asset');
 $assert(1 === count(array_filter($artifactNonEntryInlineSvgAssets, static fn (array $asset): bool => 'svg' === ($asset['kind'] ?? ''))), 'non-entry artifact simple icon SVG materializes one generated image asset');
 
 $artifactInlineScript = $compiler->compile(
diff --git a/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction-base64.json b/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction-base64.json
index c60c5f5f..74ef9d23 100644
--- a/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction-base64.json
+++ b/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction-base64.json
@@ -26,19 +26,21 @@
   "expect": [
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "assets", "assert": "count", "count": 2 },
-    { "path": "assets.1.path", "assert": "equals", "value": "assets/css/source-author-46b87bf1ffe16a17.css" },
-    { "path": "assets.1.content", "assert": "contains", "value": ":where(.blocks-engine-css-owned-grid)>*{margin-block-start:0;margin-block-end:0}" },
-    { "path": "assets.0.path", "assert": "equals", "value": "index.inline.css" },
-    { "path": "assets.0.kind", "assert": "equals", "value": "css" },
-    { "path": "assets.0.role", "assert": "equals", "value": "stylesheet" },
-    { "path": "assets.0.content", "assert": "contains", "value": ":root{--accent:#c4a35a" },
-    { "path": "assets.0.content", "assert": "contains", "value": "body{background:#faf7f0;color:var(--ink)}" },
-    { "path": "assets.0.content", "assert": "contains", "value": ".card{border:1px solid var(--accent)" },
+    { "path": "assets.0.path", "assert": "equals", "value": "assets/css/engine-support-before-author-46b87bf1ffe16a17.css" },
+    { "path": "assets.0.source", "assert": "equals", "value": "engine-support" },
+    { "path": "assets.0.stylesheet_placement", "assert": "equals", "value": "before-author" },
+    { "path": "assets.0.content", "assert": "contains", "value": ":where(.blocks-engine-css-owned-grid)>*{margin-block-start:0;margin-block-end:0}" },
+    { "path": "assets.1.path", "assert": "equals", "value": "index.inline.css" },
+    { "path": "assets.1.kind", "assert": "equals", "value": "css" },
+    { "path": "assets.1.role", "assert": "equals", "value": "stylesheet" },
+    { "path": "assets.1.content", "assert": "contains", "value": ":root{--accent:#c4a35a" },
+    { "path": "assets.1.content", "assert": "contains", "value": "body{background:#faf7f0;color:var(--ink)}" },
+    { "path": "assets.1.content", "assert": "contains", "value": ".card{border:1px solid var(--accent)" },
     { "path": "source_reports.artifact.files_by_source.inline-style", "assert": "equals", "value": 1 },
     { "path": "source_reports.artifact.files_by_intent.style", "assert": "equals", "value": 1 },
-    { "path": "source_reports.compiled_site.theme.stylesheets.0", "assert": "equals", "value": "index.inline.css" },
-    { "path": "source_reports.materialization_plan.assets.0.target_path", "assert": "equals", "value": "index.inline.css" },
-    { "path": "source_reports.materialization_plan.assets.0.content", "assert": "contains", "value": ":root{--accent:#c4a35a" },
+    { "path": "source_reports.compiled_site.theme.stylesheets.1", "assert": "equals", "value": "index.inline.css" },
+    { "path": "source_reports.materialization_plan.assets.1.target_path", "assert": "equals", "value": "index.inline.css" },
+    { "path": "source_reports.materialization_plan.assets.1.content", "assert": "contains", "value": ":root{--accent:#c4a35a" },
     { "path": "serialized_blocks", "assert": "contains", "value": "Styled Portfolio" },
     { "path": "serialized_blocks", "assert": "contains", "value": "hero" }
   ]
diff --git a/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction.json b/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction.json
index b5c37f45..78bc379c 100644
--- a/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction.json
+++ b/php-transformer/tests/fixtures/parity/artifact-inline-style-extraction.json
@@ -26,17 +26,19 @@
   "expect": [
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "assets", "assert": "count", "count": 2 },
-    { "path": "assets.1.path", "assert": "equals", "value": "assets/css/source-author-46b87bf1ffe16a17.css" },
-    { "path": "assets.1.content", "assert": "contains", "value": ":where(.blocks-engine-css-owned-grid)>*{margin-block-start:0;margin-block-end:0}" },
-    { "path": "assets.0.path", "assert": "equals", "value": "index.inline.css" },
-    { "path": "assets.0.kind", "assert": "equals", "value": "css" },
-    { "path": "assets.0.role", "assert": "equals", "value": "stylesheet" },
-    { "path": "assets.0.content", "assert": "contains", "value": ".hero{min-height:100vh" },
+    { "path": "assets.0.path", "assert": "equals", "value": "assets/css/engine-support-before-author-46b87bf1ffe16a17.css" },
+    { "path": "assets.0.source", "assert": "equals", "value": "engine-support" },
+    { "path": "assets.0.stylesheet_placement", "assert": "equals", "value": "before-author" },
+    { "path": "assets.0.content", "assert": "contains", "value": ":where(.blocks-engine-css-owned-grid)>*{margin-block-start:0;margin-block-end:0}" },
+    { "path": "assets.1.path", "assert": "equals", "value": "index.inline.css" },
+    { "path": "assets.1.kind", "assert": "equals", "value": "css" },
+    { "path": "assets.1.role", "assert": "equals", "value": "stylesheet" },
+    { "path": "assets.1.content", "assert": "contains", "value": ".hero{min-height:100vh" },
     { "path": "source_reports.artifact.files_by_source.inline-style", "assert": "equals", "value": 1 },
     { "path": "source_reports.artifact.files_by_intent.style", "assert": "equals", "value": 1 },
-    { "path": "source_reports.compiled_site.theme.stylesheets.0", "assert": "equals", "value": "index.inline.css" },
-    { "path": "source_reports.materialization_plan.assets.0.target_path", "assert": "equals", "value": "index.inline.css" },
-    { "path": "source_reports.materialization_plan.assets.0.content", "assert": "contains", "value": ".work-grid{display:grid" },
+    { "path": "source_reports.compiled_site.theme.stylesheets.1", "assert": "equals", "value": "index.inline.css" },
+    { "path": "source_reports.materialization_plan.assets.1.target_path", "assert": "equals", "value": "index.inline.css" },
+    { "path": "source_reports.materialization_plan.assets.1.content", "assert": "contains", "value": ".work-grid{display:grid" },
     { "path": "serialized_blocks", "assert": "contains", "value": "Styled Portfolio" },
     { "path": "serialized_blocks", "assert": "contains", "value": "hero" }
   ]
diff --git a/php-transformer/tests/fixtures/parity/artifact-linked-css-layout-wrapper-style-signals.json b/php-transformer/tests/fixtures/parity/artifact-linked-css-layout-wrapper-style-signals.json
index 363ba1dd..d3ac3ceb 100644
--- a/php-transformer/tests/fixtures/parity/artifact-linked-css-layout-wrapper-style-signals.json
+++ b/php-transformer/tests/fixtures/parity/artifact-linked-css-layout-wrapper-style-signals.json
@@ -47,7 +47,7 @@
     { "path": "serialized_blocks", "assert": "contains", "value": "<article class=\"wp-block-group blocks-engine-css-owned-layout\">" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "<!-- wp:blocks-engine/author-layout" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "wp-block-blocks-engine-author-layout" },
-    { "path": "source_reports.wordpress_site_plan.assets.1.content", "assert": "contains", "value": ":where(.wp-block-group.blocks-engine-css-owned-flow)>*{margin-block-start:0;margin-block-end:0}" },
+    { "path": "source_reports.wordpress_site_plan.assets.0.content", "assert": "contains", "value": ":where(.wp-block-group.blocks-engine-css-owned-flow)>*{margin-block-start:0;margin-block-end:0}" },
     { "path": "fallbacks", "assert": "count", "count": 0 }
   ]
 }
diff --git a/php-transformer/tests/fixtures/parity/html-inline-svg-positioned-css-fill-desktop-mobile.json b/php-transformer/tests/fixtures/parity/html-inline-svg-positioned-css-fill-desktop-mobile.json
index e98802ad..6f8ed00a 100644
--- a/php-transformer/tests/fixtures/parity/html-inline-svg-positioned-css-fill-desktop-mobile.json
+++ b/php-transformer/tests/fixtures/parity/html-inline-svg-positioned-css-fill-desktop-mobile.json
@@ -22,7 +22,7 @@
     { "path": "status", "assert": "equals", "value": "success" },
     { "path": "serialized_blocks", "assert": "contains", "value": "wp-block-image be-inline-geometry-" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "\"height\":\"728.88px\"" },
-    { "path": "assets.1.content", "assert": "contains", "value": ".hero-art :where(figure)" },
-    { "path": "assets.1.content", "assert": "contains", "value": ".wp-block-image > img{display:block;width:100%;height:100%;max-width:100%;object-fit:cover" }
+    { "path": "assets.2.content", "assert": "contains", "value": ".hero-art :where(figure)" },
+    { "path": "assets.2.content", "assert": "contains", "value": ".wp-block-image > img{display:block;width:100%;height:100%;max-width:100%;object-fit:cover" }
   ]
 }
diff --git a/php-transformer/tests/fixtures/parity/html-inline-svg-sized-html-valid.json b/php-transformer/tests/fixtures/parity/html-inline-svg-sized-html-valid.json
index 4e1d20ad..04d249c8 100644
--- a/php-transformer/tests/fixtures/parity/html-inline-svg-sized-html-valid.json
+++ b/php-transformer/tests/fixtures/parity/html-inline-svg-sized-html-valid.json
@@ -35,7 +35,7 @@
     { "path": "serialized_blocks", "assert": "contains", "value": "<!-- wp:image" },
     { "path": "serialized_blocks", "assert": "contains", "value": "<!-- wp:button" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "<!-- wp:icon" },
-    { "path": "assets", "assert": "count", "count": 4 },
+    { "path": "assets", "assert": "count", "count": 5 },
     { "path": "coverage.0.fallback_count", "assert": "equals", "value": 0 }
   ]
 }
diff --git a/php-transformer/tests/fixtures/parity/html-positioned-inline-geometry-carrier.json b/php-transformer/tests/fixtures/parity/html-positioned-inline-geometry-carrier.json
index b894f310..b0fab19a 100644
--- a/php-transformer/tests/fixtures/parity/html-positioned-inline-geometry-carrier.json
+++ b/php-transformer/tests/fixtures/parity/html-positioned-inline-geometry-carrier.json
@@ -43,12 +43,12 @@
     { "path": "serialized_blocks", "assert": "not_contains", "value": "<script" },
     { "path": "serialized_blocks", "assert": "not_contains", "value": "javascript:" },
     { "path": "assets.0.content", "assert": "contains", "value": "position:absolute" },
-    { "path": "assets.0.content", "assert": "contains", "value": "z-index:2" },
+    { "path": "assets.1.content", "assert": "contains", "value": "z-index:2" },
     { "path": "assets.0.content", "assert": "contains", "value": "inset:1rem auto auto 2rem !important" },
     { "path": "assets.0.content", "assert": "contains", "value": "margin-top:0;margin-bottom:0" },
-    { "path": "assets.0.content", "assert": "contains", "value": ":where(.blocks-engine-semantic-" },
-    { "path": "assets.0.content", "assert": "contains", "value": ".x > strong::before{content:" },
-    { "path": "assets.0.content", "assert": "contains", "value": "backdrop-filter:blur(1px)" },
+    { "path": "assets.1.content", "assert": "contains", "value": ":where(.blocks-engine-semantic-" },
+    { "path": "assets.1.content", "assert": "contains", "value": ".x > strong::before{content:" },
+    { "path": "assets.1.content", "assert": "contains", "value": "backdrop-filter:blur(1px)" },
     { "path": "source_reports.wp_block_validity.status", "assert": "equals", "value": "pass" },
     { "path": "fallbacks", "assert": "count", "count": 1 }
   ]
diff --git a/php-transformer/tests/fixtures/parity/html-product-card-svg-price-grid.json b/php-transformer/tests/fixtures/parity/html-product-card-svg-price-grid.json
index 362c4edc..1ebbba79 100644
--- a/php-transformer/tests/fixtures/parity/html-product-card-svg-price-grid.json
+++ b/php-transformer/tests/fixtures/parity/html-product-card-svg-price-grid.json
@@ -34,7 +34,7 @@
     { "path": "blocks.0.innerBlocks.0.innerBlocks.0.attrs.url", "assert": "contains", "value": "assets/materialized-svg/" },
     { "path": "blocks.0.innerBlocks.0.innerBlocks.0.attrs.alt", "assert": "equals", "value": "Ceramic bowl" },
     { "path": "blocks.0.innerBlocks.0.innerBlocks.0.attrs.className", "assert": "contains", "value": "product-image be-inline-geometry-" },
-    { "path": "assets", "assert": "count", "count": 3 },
+    { "path": "assets", "assert": "count", "count": 4 },
     { "path": "serialized_blocks", "assert": "contains", "value": "product-price" },
     { "path": "source_reports.html.structure_signals.3.signals.price_like", "assert": "equals", "value": true },
     { "path": "source_reports.html.structure_signals.14.signals.grid_like", "assert": "equals", "value": true },
diff --git a/php-transformer/tests/fixtures/parity/html-structured-list-descendant-css-row-styles.json b/php-transformer/tests/fixtures/parity/html-structured-list-descendant-css-row-styles.json
index 19fe19db..510fd2fb 100644
--- a/php-transformer/tests/fixtures/parity/html-structured-list-descendant-css-row-styles.json
+++ b/php-transformer/tests/fixtures/parity/html-structured-list-descendant-css-row-styles.json
@@ -32,9 +32,9 @@
     { "path": "serialized_blocks", "assert": "contains", "value": "blocks-engine-source-li-" },
     { "path": "serialized_blocks", "assert": "contains", "value": "padding-top:0.9rem" },
     { "path": "serialized_blocks", "assert": "contains", "value": "<p class=\"track-title\">Kindling</p>" },
-    { "path": "assets.0.content", "assert": "contains", "value": ":where(.blocks-engine-source-li-" },
-    { "path": "assets.0.content", "assert": "contains", "value": "align-items:baseline" },
-    { "path": "assets.0.content", "assert": "contains", "value": "gap:1.25rem" },
+    { "path": "assets.1.content", "assert": "contains", "value": ":where(.blocks-engine-source-li-" },
+    { "path": "assets.1.content", "assert": "contains", "value": "align-items:baseline" },
+    { "path": "assets.1.content", "assert": "contains", "value": "gap:1.25rem" },
     { "path": "fallbacks", "assert": "count", "count": 0 }
   ]
 }
diff --git a/php-transformer/tests/unit/artifact-author-stylesheet-projection.php b/php-transformer/tests/unit/artifact-author-stylesheet-projection.php
index dd56adce..d5c50c00 100644
--- a/php-transformer/tests/unit/artifact-author-stylesheet-projection.php
+++ b/php-transformer/tests/unit/artifact-author-stylesheet-projection.php
@@ -28,7 +28,7 @@
 $assets = $result['assets'] ?? array();
 $assetPaths = array_column($assets, 'path');
 $assert(array( 'index.inline-1.css', 'a.css', 'index.inline-2.css', 'b.css', 'a.occurrence-2-generated-1.css', 'a.occurrence-2.css' ) === array_slice($assetPaths, 0, 6)
-    && 1 === preg_match('#^assets/css/source-author-[a-f0-9]{16}\.css$#', $assetPaths[6] ?? ''), 'allocated repeated-link alias avoids authored path collisions while preserving source occurrence order');
+    && 1 === preg_match('#^assets/css/engine-support-after-author-[a-f0-9]{16}\.css$#', $assetPaths[6] ?? ''), 'allocated repeated-link alias avoids authored path collisions while preserving source occurrence and support placement order');
 foreach ( $assets as $asset ) {
     $content = (string) ($asset['content'] ?? '');
     $hash = hash('sha256', $content);
@@ -54,7 +54,7 @@
     ),
 ) )->toArray();
 $richTextAssets = $richText['assets'] ?? array();
-$assert(str_starts_with((string) ($richTextAssets[0]['content'] ?? ''), ':where(mark)[style*="--blocks-engine-richtext-marker:"]{background-color:transparent;color:inherit}') && str_contains((string) ($richTextAssets[0]['content'] ?? ''), '{color:#e8a020}') && ! str_contains((string) ($richTextAssets[1]['content'] ?? ''), 'background-color:transparent;color:inherit'), 'artifact projection emits one marker reset before the first projected author stylesheet');
+$assert('engine-support' === ($richTextAssets[0]['source'] ?? '') && 'before-author' === ($richTextAssets[0]['stylesheet_placement'] ?? '') && str_starts_with((string) ($richTextAssets[0]['content'] ?? ''), ':where(mark)[style*="--blocks-engine-richtext-marker:"]{background-color:transparent;color:inherit}') && str_contains((string) ($richTextAssets[1]['content'] ?? ''), '{color:#e8a020}') && ! str_contains((string) ($richTextAssets[1]['content'] ?? ''), 'background-color:transparent;color:inherit'), 'artifact projection emits one marker-reset support asset before the first projected author stylesheet');
 
 $importedFont = ( new ArtifactCompiler() )->compile(array( 'files' => array(
     array( 'path' => 'index.html', 'kind' => 'html', 'content' => '<!doctype html><html><head><link rel="stylesheet" href="style.css"></head><body><p><span class="accent">Text</span></p></body></html>' ),
@@ -62,7 +62,7 @@
 ) ) )->toArray();
 $importedFontAssets = array_column($importedFont['assets'] ?? array(), null, 'path');
 $importedFontCss = (string) ($importedFontAssets['style.css']['content'] ?? '');
-$assert(str_starts_with($importedFontCss, '@import url("https://fonts.googleapis.com/css2?family=Inter");') && strpos($importedFontCss, '@import') < strpos($importedFontCss, ':where(mark)'), 'author stylesheet imports remain before generated marker and geometry rules');
+$assert(str_starts_with($importedFontCss, '@import url("https://fonts.googleapis.com/css2?family=Inter");') && ! str_contains($importedFontCss, ':where(mark)') && 'before-author' === ($importedFont['assets'][0]['stylesheet_placement'] ?? '') && 'style.css' === ($importedFont['assets'][1]['path'] ?? ''), 'author stylesheet imports retain their leading preamble while marker support loads from a preceding asset');
 
 $inlineLayoutLeaves = ( new ArtifactCompiler() )->compile(array( 'files' => array(
     array( 'path' => 'index.html', 'kind' => 'html', 'content' => '<link rel="stylesheet" href="layout.css"><div class="artifact-card"><span class="card-label">Input</span><strong>index.html</strong><span class="card-label">styles.css</span><span class="card-label">assets/</span></div><p>Ordinary <strong>prose</strong> and <span>inline text</span>.</p>' ),
@@ -200,10 +200,26 @@
         array( 'path' => 'shared.css', 'kind' => 'css', 'content' => '.quote-mark{color:#e8a020}' ),
     ),
 ) )->toArray();
-$multiPageAuthorAssets = array_values(array_filter($multiPage['assets'] ?? array(), static fn (array $asset): bool => 'author-css' === ($asset['source'] ?? '')));
-$assert(1 === count($multiPageAuthorAssets), 'identical generated author stylesheets are emitted once across HTML routes');
+$multiPageSupportAssets = array_values(array_filter($multiPage['assets'] ?? array(), static fn (array $asset): bool => 'engine-support' === ($asset['source'] ?? '')));
+$assert(1 === count($multiPageSupportAssets), 'identical generated engine support stylesheets are emitted once across HTML routes');
+$multiPageAssetPaths = array_column($multiPage['assets'] ?? array(), 'path');
+$multiPageWordPressAssets = $multiPage['source_reports']['wordpress_site_plan']['assets'] ?? array();
+$assert(1 === preg_match('#^assets/css/engine-support-before-author-[a-f0-9]{16}\.css$#', $multiPageAssetPaths[0] ?? '') && 'shared.css' === ($multiPageAssetPaths[1] ?? '') && 'shared' === ($multiPageSupportAssets[0]['compilation']['scope'] ?? '') && 'global' === ($multiPageWordPressAssets[0]['scopes'][0]['kind'] ?? ''), 'identical multi-page support is ordered before author CSS and promoted to global scope');
 $assert('blocks-engine/wordpress-site-plan/v2' === ($multiPage['source_reports']['wordpress_site_plan']['schema'] ?? null), 'deduplicated multi-route assets produce a canonical WordPress site plan');
 
+$siblingSupport = ( new ArtifactCompiler() )->compile(array(
+    'entrypoint' => 'index.html',
+    'files' => array(
+        array( 'path' => 'index.html', 'kind' => 'html', 'content' => '<link rel="stylesheet" href="index.css"><main><p>Home</p></main>' ),
+        array( 'path' => 'about.html', 'kind' => 'html', 'content' => '<link rel="stylesheet" href="about.css"><main><div class="grid"><div>A</div><div>B</div></div></main>' ),
+        array( 'path' => 'index.css', 'kind' => 'css', 'content' => 'p{margin:0}' ),
+        array( 'path' => 'about.css', 'kind' => 'css', 'content' => '.grid{display:grid;grid-template-columns:1fr 1fr}' ),
+    ),
+) )->toArray();
+$siblingSupportAssets = $siblingSupport['assets'] ?? array();
+$siblingWordPressAssets = $siblingSupport['source_reports']['wordpress_site_plan']['assets'] ?? array();
+$assert(1 === preg_match('#^assets/css/engine-support-before-author-[a-f0-9]{16}\.css$#', (string) ($siblingSupportAssets[0]['path'] ?? '')) && 'before-author' === ($siblingSupportAssets[0]['stylesheet_placement'] ?? '') && 'index.css' === ($siblingSupportAssets[1]['path'] ?? '') && 'about.css' === ($siblingSupportAssets[2]['path'] ?? '') && 'about.html' === ($siblingSupportAssets[0]['compilation']['id'] ?? '') && 'about.html' === ($siblingWordPressAssets[0]['scopes'][0]['source_path'] ?? ''), 'non-entry page support stays page-scoped and precedes every author stylesheet');
+
 $externalLayouts = ( new ArtifactCompiler() )->compile(array(
     'entrypoint' => 'index.html',
     'files' => array(
@@ -315,7 +331,7 @@
 $assert(preg_match('/<figure class="wp-block-table (blocks-engine-table-[^"]+)">/', $tableNormalizationMarkup, $tableNormalizationMarker) === 1, 'native table normalization uses an isolated table marker');
 $tableCellReset = '.' . ($tableNormalizationMarker[1] ?? '') . '>table th,.' . ($tableNormalizationMarker[1] ?? '') . '>table td{border:0}';
 $tableBottomBorder = '.' . ($tableNormalizationMarker[1] ?? '') . '>table>tbody>tr:nth-child(1)>td:nth-child(1)';
-$assert(str_contains($tableNormalizationCss, '.' . ($tableNormalizationMarker[1] ?? '') . '{margin:0}') && ! str_contains($tableNormalizationCss, '.wp-block-table.' . ($tableNormalizationMarker[1] ?? '') . '{margin:0}') && str_contains($tableNormalizationCss, '.' . ($tableNormalizationMarker[1] ?? '') . '>table{border-collapse:collapse;border-spacing:0}') && str_contains($tableNormalizationCss, $tableCellReset) && str_contains($tableNormalizationCss, '.' . ($tableNormalizationMarker[1] ?? '') . '>table>thead{border-bottom:0}') && false !== strpos($tableNormalizationCss, $tableCellReset) && false !== strpos($tableNormalizationCss, $tableBottomBorder) && strpos($tableNormalizationCss, $tableBottomBorder) < strpos($tableNormalizationCss, $tableCellReset) && str_contains($tableNormalizationCss, $tableBottomBorder . ':not(blocks-engine-specificity-'), 'collapsed border tables clear all synthetic cell sides while the more-specific projected bottom-only rules restore the source geometry');
+$assert(str_contains($tableNormalizationCss, '.' . ($tableNormalizationMarker[1] ?? '') . '{margin:0}') && ! str_contains($tableNormalizationCss, '.wp-block-table.' . ($tableNormalizationMarker[1] ?? '') . '{margin:0}') && str_contains($tableNormalizationCss, '.' . ($tableNormalizationMarker[1] ?? '') . '>table{border-collapse:collapse;border-spacing:0}') && str_contains($tableNormalizationCss, $tableCellReset) && str_contains($tableNormalizationCss, '.' . ($tableNormalizationMarker[1] ?? '') . '>table>thead{border-bottom:0}') && false !== strpos($tableNormalizationCss, $tableCellReset) && false !== strpos($tableNormalizationCss, $tableBottomBorder) && strpos($tableNormalizationCss, $tableCellReset) < strpos($tableNormalizationCss, $tableBottomBorder) && str_contains($tableNormalizationCss, $tableBottomBorder . ':not(blocks-engine-specificity-'), 'collapsed border tables clear all synthetic cell sides before projected bottom-only author rules restore the source geometry');
 $assert(str_contains($tableNormalizationCss, '.table-wrap{margin-bottom:2rem}') && str_contains($tableNormalizationCss, 'table{margin:3rem 0}') && str_contains($tableNormalizationCss, 'table{border-collapse:collapse;border-spacing:0}'), 'authored wrapper and table margins remain in the source stylesheet rather than becoming a broad table override');
 $assert('pass' === ( new Runtime() )->validateBlockSerialization($tableNormalizationMarkup)['status'], 'table normalization preserves editor-valid native markup');
 
diff --git a/php-transformer/tests/unit/author-selector-semantics.php b/php-transformer/tests/unit/author-selector-semantics.php
index c2760ce5..6c90308b 100644
--- a/php-transformer/tests/unit/author-selector-semantics.php
+++ b/php-transformer/tests/unit/author-selector-semantics.php
@@ -17,12 +17,13 @@
 };
 $transform = static fn (string $html): array => ( new HtmlTransformer() )->transform($html)->toArray();
 $css = static function (array $result): string {
+    $parts = array();
     foreach ( $result['assets'] ?? array() as $asset ) {
         if ( 'css' === ($asset['kind'] ?? '') ) {
-            return (string) ($asset['content'] ?? '');
+            $parts[] = (string) ($asset['content'] ?? '');
         }
     }
-    return '';
+    return implode("\n", $parts);
 };
 
 $paragraph = $transform('<style>p{color:red}span{color:blue}</style><span>Loose text</span><p>Paragraph</p>');
@@ -211,7 +212,24 @@
 $richTextColor = $transform('<style>:root{--amber:#e8a020}.quote-mark{font-size:4rem;color:var(--amber)}</style><p><span class="quote-mark">&quot;</span>Testimonial</p>');
 $richTextColorMarkup = (string) ($richTextColor['serialized_blocks'] ?? '');
 $richTextColorCss = $css($richTextColor);
-$assert(str_contains($richTextColorMarkup, '--blocks-engine-richtext-marker:blocks-engine-richtext-') && ! str_contains($richTextColorMarkup, 'color:inherit') && ! str_contains($richTextColorMarkup, 'background-color:transparent') && str_contains($richTextColorCss, ':where(mark)[style*="--blocks-engine-richtext-marker:"]{background-color:transparent;color:inherit}') && str_contains($richTextColorCss, '{font-size:4rem;color:var(--amber)}') && strpos($richTextColorCss, 'color:inherit') < strpos($richTextColorCss, 'color:var(--amber)'), 'RichText marker reset stays below projected author paint instead of overriding it inline');
+$assert(str_contains($richTextColorMarkup, '--blocks-engine-richtext-marker:blocks-engine-richtext-') && ! str_contains($richTextColorMarkup, 'color:inherit') && ! str_contains($richTextColorMarkup, 'background-color:transparent') && str_contains($richTextColorCss, ':where(mark)[style*="--blocks-engine-richtext-marker:"]{background-color:transparent;color:inherit}') && str_contains($richTextColorCss, '{font-size:4rem;color:var(--amber)}') && strpos($richTextColorCss, 'color:inherit') < strpos($richTextColorCss, 'color:var(--amber)'), 'RichText marker defers transparent background to the preceding reset CSS while explicit author color remains authoritative');
+
+$markStaticLonghand = $transform('<style>.hl{background-color:gold}</style><p><span class="hl">Static longhand</span></p>');
+$markStaticLonghandMarkup = (string) ($markStaticLonghand['serialized_blocks'] ?? '');
+$assert(str_contains($markStaticLonghandMarkup, '<mark class="hl"') && str_contains($markStaticLonghandMarkup, 'background-color:gold') && ! str_contains($markStaticLonghandMarkup, 'background-color:transparent'), 'authored static longhand background survives RichText mark projection');
+
+$markStaticShorthand = $transform('<style>.hl{background:gold}</style><p><span class="hl">Static shorthand</span></p>');
+$markStaticShorthandMarkup = (string) ($markStaticShorthand['serialized_blocks'] ?? '');
+$assert(str_contains($markStaticShorthandMarkup, '<mark class="hl"') && str_contains($markStaticShorthandMarkup, 'background:gold') && ! str_contains($markStaticShorthandMarkup, 'background-color:transparent'), 'authored static shorthand background survives RichText mark projection');
+
+$markConditionalLonghand = $transform('<style>@media(min-width:1px){.hl{background-color:gold}}</style><p><span class="hl">Conditional longhand</span></p>');
+$markConditionalLonghandMarkup = (string) ($markConditionalLonghand['serialized_blocks'] ?? '');
+$markConditionalLonghandCss = $css($markConditionalLonghand);
+$assert(str_contains($markConditionalLonghandMarkup, '<mark class="hl"') && str_contains($markConditionalLonghandCss, '@media(min-width:1px)') && str_contains($markConditionalLonghandCss, 'background-color:gold') && ! str_contains($markConditionalLonghandMarkup, 'background-color:transparent'), 'authored conditional longhand background survives RichText mark projection');
+
+$markInlineLonghand = $transform('<p><span class="hl" style="background-color:gold">Inline longhand</span></p>');
+$markInlineLonghandMarkup = (string) ($markInlineLonghand['serialized_blocks'] ?? '');
+$assert(str_contains($markInlineLonghandMarkup, '<mark class="hl"') && str_contains($markInlineLonghandMarkup, 'background-color:gold') && ! str_contains($markInlineLonghandMarkup, 'background-color:transparent'), 'authored inline longhand background survives RichText mark projection');
 
 $richTextPunctuation = $transform('<style>.quote-mark{font-size:4rem}</style><p><span class="quote-mark">"</span>The team\'s launch</p>');
 $richTextPunctuationMarkup = (string) ($richTextPunctuation['serialized_blocks'] ?? '');
diff --git a/php-transformer/tests/unit/engine-support-css-asset.php b/php-transformer/tests/unit/engine-support-css-asset.php
new file mode 100644
index 00000000..44685037
--- /dev/null
+++ b/php-transformer/tests/unit/engine-support-css-asset.php
@@ -0,0 +1,241 @@
+<?php
+declare(strict_types=1);
+
+require dirname(__DIR__, 2) . '/vendor/autoload.php';
+
+use Automattic\BlocksEngine\PhpTransformer\ArtifactCompiler\ArtifactCompiler;
+use Automattic\BlocksEngine\PhpTransformer\HtmlToBlocks\HtmlTransformer;
+
+$failures = 0;
+$passes = 0;
+
+$assert = static function (bool $condition, string $message) use (&$failures, &$passes): void {
+    if ( $condition ) {
+        ++$passes;
+        return;
+    }
+
+    ++$failures;
+    fwrite(STDERR, "FAIL: {$message}\n");
+};
+
+/** @return array<int,array<string,mixed>> */
+$cssAssets = static fn (array $result): array => array_values(array_filter(
+    is_array($result['assets'] ?? null) ? $result['assets'] : array(),
+    static fn (array $asset): bool => 'css' === ($asset['kind'] ?? '')
+));
+
+/** @return array<int,array<string,mixed>> */
+$sourceAssets = static fn (array $result, string $source): array => array_values(array_filter(
+    is_array($result['assets'] ?? null) ? $result['assets'] : array(),
+    static fn (array $asset): bool => $source === ($asset['source'] ?? '')
+));
+
+$cssFor = static function (array $result, string $source, ?string $placement = null) use ($sourceAssets): string {
+    $assets = $sourceAssets($result, $source);
+    if ( null !== $placement ) {
+        $assets = array_values(array_filter(
+            $assets,
+            static fn (array $asset): bool => $placement === ($asset['stylesheet_placement'] ?? '')
+        ));
+    }
+
+    return implode("\n", array_map(static fn (array $asset): string => (string) ($asset['content'] ?? ''), $assets));
+};
+
+$authorOrder = ( new HtmlTransformer() )->transform(
+    '<style>@layer contract;.contract-author-only{color:#123456}.desktop-nav a{color:#fff}.btn{display:inline-flex;padding:1rem;background:#123456;width:100%}@media(max-width:700px){.desktop-nav{display:none}.mobile-nav{background:rgba(0,0,0,.9)}}</style>'
+        . '<nav class="desktop-nav"><ul><li><a href="/">Home</a></li><li><a href="/about">About</a></li></ul></nav>'
+        . '<div class="mobile-nav"><nav><ul><li><a href="/">Home</a></li><li><a href="/about">About</a></li></ul></nav></div>'
+        . '<p class="contract-author-only">Contract</p><main><section><a class="btn" href="/submit">Submit</a></section></main>'
+)->toArray();
+
+$authorAssets = $sourceAssets($authorOrder, 'author-css');
+$assert(1 === count($authorAssets), 'G2: transform emits exactly one author-css asset');
+$normalizedAuthorCss = preg_replace('/\s+/', '', (string) ($authorAssets[0]['content'] ?? '')) ?? '';
+$assert(
+    '@layercontract;.contract-author-only{color:#123456}.desktop-nava{color:#fff}:where(.blocks-engine-control-6494fb2a0d77-3):not(.blocks-engine-specificity-class-6494fb2a0d77-1)>:where(.wp-block-button__link){display:inline-flex;padding:1rem;background:#123456;width:100%}@media(max-width:700px){.desktop-nav{display:none}.mobile-nav{background:rgba(0,0,0,.9)}}' === $normalizedAuthorCss,
+    'G2: author-css contains only its leading at-rule preamble and rewritten author stylesheet'
+);
+$assert('author' === ($authorAssets[0]['stylesheet_placement'] ?? ''), 'G4: author-css record declares author placement');
+
+$geometry = ( new HtmlTransformer() )->transform(
+    '<main><p id="target" style="width:30rem">Geometry</p></main>',
+    array( 'static_css' => '#target{width:12rem}' )
+)->toArray();
+$richText = ( new HtmlTransformer() )->transform(
+    '<style>.maintenance-loop{display:grid}.maintenance-loop li > span{display:inline-block;width:10px;height:10px;border-radius:50%;background:#e8a020}</style>'
+        . '<ul class="maintenance-loop"><li><span>Build</span></li></ul>'
+)->toArray();
+$synthetic = ( new HtmlTransformer() )->transform(
+    '<style>p{margin:0}.site-header{display:flex;align-items:center}.brand{font-size:18px;font-weight:700}</style>'
+        . '<header class="site-header"><a class="brand" href="/">Verified Artifact</a></header><footer><span>Portable input.</span></footer><p>Source paragraph.</p>'
+)->toArray();
+$inlineLayout = ( new HtmlTransformer() )->transform(
+    '<style>.artifact-card{display:grid;grid-template-columns:1fr auto}.artifact-card > strong{display:block;margin:12px 0 4.8px}.artifact-card .card-label{display:block;grid-column:1 / -1;color:#6040cc;margin:2px 0}</style>'
+        . '<div class="artifact-card"><span class="card-label">Input</span><strong>index.html</strong><span class="card-label">styles.css</span></div>'
+)->toArray();
+$layoutItems = ( new ArtifactCompiler() )->compile(array(
+    'entrypoint' => 'index.html',
+    'files' => array(
+        array( 'path' => 'index.html', 'kind' => 'html', 'content' => '<link rel="stylesheet" href="styles.css"><main><div class="hero-visual"><div class="artifact-card"><span class="card-label">Input</span><strong>index.html</strong><span>styles.css</span><span>assets/</span></div></div></main>' ),
+        array( 'path' => 'styles.css', 'kind' => 'css', 'content' => '.hero-visual{display:grid;gap:2rem}.artifact-card{display:grid;grid-template-columns:1fr auto}.artifact-card > span:not(.card-label){grid-column:2}.artifact-card > strong{grid-column:1}.artifact-card .card-label{grid-column:1 / -1}' ),
+    ),
+) )->toArray();
+$positionedLink = ( new HtmlTransformer() )->transform(
+    '<style>.skip-link{position:fixed;top:-200px;left:0;padding:12px 18px;background:#135e96;color:#fff;border-radius:999px}.skip-link:focus{top:0}</style>'
+        . '<a class="skip-link" href="#content">Skip to content</a><main id="content">Content</main>'
+)->toArray();
+$emptyFlex = ( new HtmlTransformer() )->transform(
+    '<style>.utils{display:flex}.placeholder{visibility:hidden;height:80px}</style><div class="utils"><span>Action</span><div class="placeholder"></div></div>'
+)->toArray();
+$nativeSearch = ( new HtmlTransformer() )->transform(
+    '<style>.search-icon{display:none;height:80px}.search-icon.visible{display:block}</style><script>document.querySelector(".search-icon").classList.add("visible")</script>'
+        . '<header><div class="site-utils"><span class="provider-search"><form id="provider-search" action="/apps/search" method="get"><input type="text" name="q" placeholder="Search"></form></span><button class="search-icon"><svg width="12px" height="13px" viewBox="0 0 12 13"><path d="M1 1"></path></svg></button><button class="search-close">close</button></div></header>'
+)->toArray();
+$nativeButton = ( new HtmlTransformer() )->transform(
+    '<style>.cta{display:inline-block;border:1px solid #000}.cta .cta-inner{display:inline-block;min-width:170px;padding:22px 26px;background-color:#00ff8e;color:#000;font-size:16px;line-height:1;font-weight:700}.highlight .cta-inner{background:#fff;color:#000}</style>'
+        . '<div style="text-align:center"><a class="cta highlight" href="/learn"><span class="cta-inner">Learn more</span></a></div>'
+)->toArray();
+$directFlexButton = ( new HtmlTransformer() )->transform(
+    '<style>.stack{display:flex;flex-direction:column;gap:2rem}.row{display:flex;align-items:center;gap:1rem;padding:1rem;background:#123456}.row__name{flex:1}</style>'
+        . '<main><div class="stack"><a class="row" href="/product"><span class="row__name">Product</span><span>$25</span></a></div></main>'
+)->toArray();
+$fullWidthButton = ( new HtmlTransformer() )->transform(
+    '<style>.btn{display:inline-flex;align-items:center;padding:1rem;background:#123456}.btn--full{width:100%}</style>'
+        . '<main><section><a class="btn btn--full selector-submit" href="/submit">Submit</a></section></main>'
+)->toArray();
+
+$results = array(
+    $authorOrder,
+    $geometry,
+    $richText,
+    $synthetic,
+    $inlineLayout,
+    $layoutItems,
+    $positionedLink,
+    $emptyFlex,
+    $nativeSearch,
+    $nativeButton,
+    $directFlexButton,
+    $fullWidthButton,
+);
+$beforeCss = '';
+$afterCss = '';
+$authorCss = '';
+foreach ( $results as $result ) {
+    $beforeCss .= "\n" . $cssFor($result, 'engine-support', 'before-author');
+    $afterCss .= "\n" . $cssFor($result, 'engine-support', 'after-author');
+    $authorCss .= "\n" . $cssFor($result, 'author-css');
+}
+
+$beforeFamilies = array(
+    'be-inline-geometry' => '.be-inline-geometry-',
+    'richtext-marker reset' => ':where(mark)[style*="--blocks-engine-richtext-marker:"]{background-color:transparent;color:inherit}',
+    'synthetic-paragraph' => ':where(.blocks-engine-synthetic-paragraph){margin-top:0;margin-bottom:0}',
+    'synthetic-anchor-undecorated' => 'blocks-engine-synthetic-anchor-undecorated',
+    'inline-layout-carrier' => ':where(p.blocks-engine-inline-layout-carrier){display:contents;margin:0!important;padding:0!important;border:0!important}',
+    'css-owned-flow paragraph' => ':where(.blocks-engine-css-owned-flow)>p{margin-top:0;margin-bottom:0}',
+    'css-owned-flow direct children' => ':where(.wp-block-group.blocks-engine-css-owned-flow)>*{margin-block-start:0;margin-block-end:0}',
+    'css-owned-grid' => ':where(.blocks-engine-css-owned-grid)>*{margin-block-start:0;margin-block-end:0}',
+    'css-owned-layout-item' => ':where(.wp-block-group.blocks-engine-css-owned-layout-item)>*{margin-block-start:0;margin-block-end:0}',
+    'positioned-fragment-link-carrier' => ':where(.blocks-engine-positioned-fragment-link-carrier){display:contents!important}',
+    'empty-flex-item' => ':where(.blocks-engine-empty-flex-item){flex:0 0 0!important;width:0!important;min-width:0!important;margin-left:0!important;margin-right:0!important}',
+    'list-navigation base' => '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation-item.wp-block-navigation-link{display:list-item;font:inherit}',
+    'nativeSearchTriggerCssRules' => 'flex:0 0 24px!important;width:24px!important;height:80px!important',
+);
+$afterFamilies = array(
+    'list-navigation host' => '.wp-block-navigation.blocks-engine-list-navigation{display:flex!important}',
+    'list-navigation mobile overlay' => '.wp-block-navigation.blocks-engine-list-navigation .wp-block-navigation__responsive-container.is-menu-open{background:rgba(0,0,0,.9)!important}',
+    'nativeButtonStyleRules' => 'background-color:#fff!important;color:#000!important',
+    'directFlexButtonStyleRules' => '.wp-block-buttons){display:block!important;gap:0!important;min-width:0;width:100%!important}',
+    'fullWidthButtonStyleRules' => '.wp-block-buttons){display:block!important;gap:0!important;width:100%!important}',
+);
+foreach ( $beforeFamilies as $family => $needle ) {
+    $assert(str_contains($beforeCss, $needle), 'G3: ' . $family . ' lives in before-author engine-support');
+    $assert(! str_contains($authorCss, $needle), 'G3: ' . $family . ' does not leak into author-css');
+}
+foreach ( $afterFamilies as $family => $needle ) {
+    $assert(str_contains($afterCss, $needle), 'G3: ' . $family . ' lives in after-author engine-support');
+    $assert(! str_contains($authorCss, $needle), 'G3: ' . $family . ' does not leak into author-css');
+}
+
+$orderedCssAssets = $cssAssets($authorOrder);
+$beforeIndex = null;
+$authorIndex = null;
+$afterIndex = null;
+foreach ( $orderedCssAssets as $index => $asset ) {
+    if ( 'engine-support' === ($asset['source'] ?? '') && 'before-author' === ($asset['stylesheet_placement'] ?? '') ) {
+        $beforeIndex = $index;
+    }
+    if ( 'author-css' === ($asset['source'] ?? '') ) {
+        $authorIndex = $index;
+    }
+    if ( 'engine-support' === ($asset['source'] ?? '') && 'after-author' === ($asset['stylesheet_placement'] ?? '') ) {
+        $afterIndex = $index;
+    }
+}
+$assert(is_int($beforeIndex) && is_int($authorIndex) && is_int($afterIndex) && $beforeIndex < $authorIndex && $authorIndex < $afterIndex, 'G4: direct transform preserves before-author, author, after-author asset order');
+$assert(str_contains((string) ($orderedCssAssets[$beforeIndex]['content'] ?? ''), 'blocks-engine-list-navigation') && str_contains((string) ($orderedCssAssets[$afterIndex]['content'] ?? ''), 'blocks-engine-list-navigation'), 'G4: split list-navigation rules retain both cascade sides');
+
+$navArtifact = ( new ArtifactCompiler() )->compile(array(
+    'entry' => 'index.html',
+    'files' => array(
+        'index.html' => '<!doctype html><html><head><link rel="stylesheet" href="styles.css"></head><body><nav class="desktop-nav"><ul><li><a href="/">Home</a></li><li><a href="/about">About</a></li></ul></nav><div class="mobile-nav"><nav><ul><li><a href="/">Home</a></li><li><a href="/about">About</a></li></ul></nav></div></body></html>',
+        'styles.css' => '.desktop-nav a{color:#fff}@media(max-width:700px){.desktop-nav{display:none}.mobile-nav{background:rgba(0,0,0,.9)}}',
+    ),
+) )->toArray();
+$navAssets = $navArtifact['assets'] ?? array();
+$navBeforeIndex = null;
+$navAuthorIndex = null;
+$navAfterIndex = null;
+foreach ( $navAssets as $index => $asset ) {
+    if ( 'engine-support' === ($asset['source'] ?? '') && 'before-author' === ($asset['stylesheet_placement'] ?? '') ) {
+        $navBeforeIndex = $index;
+    }
+    if ( 'styles.css' === ($asset['path'] ?? '') ) {
+        $navAuthorIndex = $index;
+    }
+    if ( 'engine-support' === ($asset['source'] ?? '') && 'after-author' === ($asset['stylesheet_placement'] ?? '') ) {
+        $navAfterIndex = $index;
+    }
+}
+$assert(is_int($navBeforeIndex) && is_int($navAuthorIndex) && is_int($navAfterIndex) && $navBeforeIndex < $navAuthorIndex && $navAuthorIndex < $navAfterIndex, 'G4: ArtifactCompiler preserves generated support around manifest author CSS');
+
+foreach ( array( 'compiled_site', 'materialization_plan', 'wordpress_site_plan' ) as $reportName ) {
+    $reportAssets = $navArtifact['source_reports'][$reportName]['assets'] ?? array();
+    $supportRows = array_values(array_filter(
+        is_array($reportAssets) ? $reportAssets : array(),
+        static fn (array $asset): bool => 'engine-support' === ($asset['source'] ?? '')
+    ));
+    $placements = array_column($supportRows, 'stylesheet_placement');
+    $assert(in_array('before-author', $placements, true) && in_array('after-author', $placements, true), 'G4: ' . $reportName . ' exposes support placement without parsing CSS');
+}
+
+$neutralizer = '.wp-block-group.blocks-engine-css-owned-layout>:where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width:none!important;margin-left:0!important;margin-right:0!important}';
+$layoutCssSurfaces = array($beforeCss);
+foreach ( array( 'compiled_site', 'materialization_plan', 'wordpress_site_plan' ) as $reportName ) {
+    foreach ( $layoutItems['source_reports'][$reportName]['assets'] ?? array() as $asset ) {
+        if ( is_array($asset) && 'css' === ($asset['kind'] ?? '') ) {
+            $layoutCssSurfaces[] = (string) ($asset['content'] ?? '');
+        }
+    }
+}
+$assert(! str_contains(implode("\n", $layoutCssSurfaces), $neutralizer), 'G5: css-owned-layout neutralizer is absent from every compiler output');
+$assert(! str_contains((string) ($layoutItems['serialized_blocks'] ?? ''), 'max-width:none!important'), 'G5: css-owned-layout neutralizer is absent from serialized block markup');
+
+$richTextMarkup = (string) ($richText['serialized_blocks'] ?? '');
+$assert(
+    1 === preg_match('/<mark\b[^>]*style="[^"]*--blocks-engine-richtext-marker:[^"]*"/', $richTextMarkup)
+        && ! str_contains($richTextMarkup, 'background-color:transparent')
+        && ! str_contains($richTextMarkup, 'color:inherit'),
+    'G6: richtext-marker mark defers neutral background and color to engine support CSS'
+);
+$assert(str_contains($beforeCss, ':where(mark)[style*="--blocks-engine-richtext-marker:"]{background-color:transparent;color:inherit}'), 'G6: richTextMarkerResetCss remains in engine-support');
+
+if ( $failures > 0 ) {
+    fwrite(STDERR, "Engine support CSS asset contract: {$failures} failed, {$passes} passed\n");
+    exit(1);
+}
+
+fwrite(STDOUT, "Engine support CSS asset contract passed: {$passes} assertions\n");